Mitral stenosis is often asymptomatic early in disease until the mitral valve area decreases enough to cause a large increase in left atrial pressure. The first symptoms of MS occur on exertion as explained above. This occurs since the mitral valve area is fixed and the cardiac output is unable to increase enough above resting (a low cardiac reserve is present), and high pressures are transmitted to the pulmonary vasculature since left atrial pressures increase exponentially on exertion. This transmission of pressures results in exertional dyspnea. Fatigue and inability to exercise are also common complaints. Signs of left heart failure such as paroxysmal nocturnal dyspnea and orthopnea can occur. Symptoms of heart failure with concomitant mitral stenosis also occur in disease states that require an increased cardiac output for the same reason such as pregnancy, anemia, sepsis and thyrotoxicosis.
Most patients with moderate to severe mitral stenosis will have some degree left atrial enlargement (LAE) due to the chronic increased LA pressures. This predisposes them to atrial fibrillation. Since people with mitral stenosis rely on atrial contraction for about 20% of their cardiac output and since tachycardia decreases diastolic filling time, the onset of atrial fibrillation with a rapid ventricular rate and loss of atrial contraction results in significant symptoms of low cardiac output and heart failure. These include fatigue, dyspnea, lightheadedness, and even syncope.
In the absence of atrial fibrillation, patients with mitral stenosis still have an increased risk of thrombus formation in their left atrial due to stagnation of blood. This may lead to embolic events including stroke, acute myocardial infarction, acute mesenteric ischemia, or "Blue toe syndrome".
Hemoptysis may occur due to sudden rupture of a bronchial vein. This phenomenon is termed "pulmonary apoplexy". Ortner syndrome may occur when a massively enlarged left atrium compresses the left recurrent laryngeal nerve leading to a hoarse voice. Chest pain from right sided heart strain may occur due to severe venous pulmonary hypertension. Other signs of right heart failure such as right upper quadrant pain (due to hepatic congestion) and peripheral edema may occur.
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